Snap switch having presetting means responsive to current flow



1 1963 I KJELLMAN 3,100,826

SNAP SWITCH HAVING PRESETTING MEANS RESPONSIVE TO CURRENT FLOW FiledApril 11, 1960 4 Sheets-Sheet 1 FIG. 1..

INVENTOR THOMAS K KJELLMAN ATTORNEY SNAP SWITCH HAVING PRESETTING MEANSRESPONSIVE TO CURRENT FLOW Filed April 11, 1960 Aug. 13, 1963 T. K.KJELLMAN I 4 Sheets-Sheet 2 FIG. 2,.

1o INVENTOR THOMAS K. KJELLMAN-.

ATTORNEY 1963. 'r. K. KJELLMAN I 3,100,826 .SNAP SWITCH HAVINGPRESETTING MEANS RESPONSIVE Tb CURRENT FLOW Filed April 11, 1960 Q 4Sheets-Sheet s FIG. 8. I

l/l/l/l/l/l/l/l/l/l/l/l/l/l/l/l/l/l/l/ INVENTOR THOMAS K. KJELLMANATTRNEY Aug. 13, 1963 T. K. KJELLMAN 0,

' SNAP SWITCH HAVING PRESETTING MEANS RESPONSIVE T0 CURRENT FLOW FiledApril 11, 1960 4 Sheets-Sheet 4 13'. FIG 9.

ATTORNEY -to the return side of the line. .not affect the contour of theswitch blade since its prefer- United States Patent 3,100,826 SNAISWITCH HAVING PRESETTING MEANS RESPONSIVE T0 CUNT FLOW Thomas K.Kjellman, Timoninm, Md, assignor to The Bendix Corporation, acorporation of Delaware Filed Apr. 11, I960, er. No. 21,334 9 Claims.(ill. Mil-113) This invention relatesto electrical switches of that typewhich utilize a temperature or current-responsive device such as :abimetal strip to assist or control the switching operation; it isparticularly adapted for, but not limited to, sensitive instruments suchas humidistats, thermostats and the like wherein the sensing elementcontrols a quickacting toggle or snap switch to avoid sparking at thecontacts, with resultant contact erosion.

An object of the invention is to provide a switch of the type specifiedwherein almost one hundred percent of the work required to throw theswitch is performed by the line current, leaving practically zero workfor the sensing element to effect the final switching operation, while.at'the same time all the advantages of a snap or toggle action areretained with practically unlimited contact forces available to meetdesign specifications.

Another object is to provide a highly sensitive snap 3,100,826 PatentedAug. 13, I963 ice ' the travel of the power element with respect to theswitch switch capable of handling heavy-duty switching, and a this witha minimumI R drop across the switch.

Another object is to provide a relatively simple snap switch whicheffects a self-cleaning or wiping action between contacts during eachswitching cycle.

Another object is to provide a switch assembly particularly adapted forinstruments such as humidistats, thermostats and the like utilizingsensing elements wherein a relatively small amount of work is availableto obtain sensitivity.

A further object is to provide an improved humidity and/ or temperaturesensing and control instrument.

In attaining the foregoing objects, a conductive thermal arm or bar (inpractice a strip of bimetal) is interposed in the control circuit andhas located on the movable end or other movable portion thereof a pairof contact members spaced to meet switch-throwing requirements. Thesecontacts remain in fixed spaced relation but move bodily with said armwhen it responds to current flow and when it cools following currentcut-off. This arm may be aptly termed a switdh-presetting power elementsince it presets the actual switching member for the finalswitchthrowing act and it does practically all the switching work. Theswitching member is in the form of a snapvaction switch blade havingcoacting contacts movable between the said power element contacts. Thisswitch blade may be of the conventional toggle or snap type which as itapproaches its dead-center position requires a progressively-increasingactuating force but needs only a relatively small force to throw it pastsuch position; it is preferably located in the control circuit posteriorof and .in series with the motor or other device to be controlled,

so that when on contact is made, the current flows through the switchblade and the power arm or bar back This flow of current does either onor off contact is made, and this movement continues until the thermalpower arm or element is broughtup against adjustable stop means whichlimits blade throw line. At this point the switch blade is almost to itsdead-center position, requiring a minimum of force to throw it past deadcenter against the opposite contact.

. of the various parts of the switch are readily adaptable for bothheavy and light duty installations; it (the switch) can take a highinitial flow of current without danger of destruction simply bysubstituting the proper type. of

thermal power arm or element. As the respective parts of the switch gothrough the switching cycle, the contacts rub againstone another with aresultant wiping or cleaning action which breaks, in shear, welds due toan initial inrush of current and deters contact erosion.

The foregoing and other objects and advantages will become apparent inview of the following description taken in conjunction with thedrawings, wherein:

FIG. 1 is a view in perspective of a combined temperature and relativehumidity controller embodying the features of the invention;

FIG. 2 is a top plan view thereof;

FIG. 3 is a view in section and side elevation with the facing side wallremoved;

FIG. 4 is a view in end elevation partly broken away;

FIG. 5 is a view taken substantially on the line 5--5, FIG. 3;

FIG. 6 is a view of the base assembly taken substantially on the line6-6, FIG. 3;

FIG. 7 is a view of the said base assembly as in FIG. 6 but with theswitch blade and coacting parts removed to expose thetemperature-responsive power member;

FIG. 8 is a view similar to FIG. 7 but showing the power member removedto expose the excess current shunt bar;

51G. 9 is a plan view of the leaf spring switch member; an

FIGS. 10 to 10d are diagrammatic representations of theswitch as itundergoes the switching cycle. The improved switch is shown installed ina humidity and relative temperature controldevice which can eitherfunction as a thermostat, a humidistat, or a combined thermostat andhumidistat, i.e., it can regulate temperature as a function of relativehumidity. The working parts are encased as best shown in FIGS. '1 and 3;the switch assembly proper being located in a bottom case, here shown asbeing made up of a molded plastic topsection 10 and a base 10' fittedinto the open bottom of the section 10. Removably fitted over thesection 10' is a metallic case or shell 11, secured in place by smallscrew bolts 12.

The switch proper comprises a leaf spring switch blade of the toggle orsnap type, note FIG. 9, made of conductive material such as sheetcopper; and since the instrument is here shown adapted to sense bothtemperature and relative humidity, two of these blades 13 and 13' areutilized, :each blade being identical in construction and hence likeparts in each blade bear like reference numerals. The rear (leftllandend as viewed in FIG. 9)

ends of the blades terminate in a common integral anchoring section.'llhe manner in which these blades perform is well known although thespecific structure tfior carrying 17. Each one of the switch blades isformed with a slot '18, to accommodate connecting or banger brackets forthe humidity and temperature elements in a manner to be described. Aplate '19 overlies both switch blades and at its front end is formedwith downturned abutment members 19', one rfior each blade, while itsopposite end is secured to the said base by the screws. 17. Eachdownturned abutment 19 is notched as at 20, and the free end edge ofeach bowed spring tongue 14' engages in these notches. The notch 20 isso ocated with respect to the axial line of thrust of the tongue 14' andthe point of connection of the blade to its actuator (here thehumidityresponsive element 31 or temperature-responsive element 46, tobe described) that whenthe latter point passes through the bladesover-center thrust line in either a contact make or break direction, thecontact-carryingsec- .tion. or extremity 14 will snap to contact make or.break position. The contacts 16 and 21 or 15 and 22, however, remain inengagement until the said point of connection flexes past dead center ineither direction. The term snap switc as used herein, refers to switchesincorporating a switch blade or resilient switch [assembly whichfunction in a generally similar manner, i.e., maintain contact untilflexed or otherwise actuated past a deadcenter position. At its rearend, the plate 19 has a tongue projecting therefrom, which is bentdownwardly and passes through a slot and terminates in an exteriorlyaccessible terminal 19".

The contacts 21 and 22 are carried on the free end of a contact presetand power bimetal arm 23, which at its one end is also fixed to the basemember by the screw bolts 17. In the present instance, the upper contact22 is fixed on the free end of the power arm 23 by means of an offsetpiece 24, secured to the arm 23 as at 24'. ln practice, the piece 24 isbendable for the purpose of adjusting the spaced relation of thecontacts. Obviously, other means may be adopted for adjustably andshiftably mounting these contacts; they could be mounted on a shiftablesupport independently of the arm 23 and moved or driven by the arm totheir respective preset positions. Adjacent the center throw line of theswitch blade 13 against stop means, which may be provided in anysuitable manner. As best shown in FIGS. 4 and 7, the stop means isprovided by laterally-projecting contact portions 25 and 25 dormed onthe bar 23, which come against abutment screws 26, 26' and 27, 27',adjustable to determine withexactitude the point where the movement ofthe arm 23 terminates in the switching operation.

, Preferably, but not necessarily, the switch is provided with means(tor shunting excess current from flowing through the power arm or bar23 in the case of a short along the longitudinal center line of'theshunt bar and at 'its far end has fixed thereto a coacting shunt contact30,

compare FIGS. 3 and 7. When current flows through the power arm or bar23 and it is deformed upwardly to preset the section 14 of the switchblade 13, contact 30 engages contact 29. That part of the power arm 23-lying between the contacts 21 and 30 plus the shunt bar 28 will (or 13')the power bimetal arm or bar 23 is brought up then make up a returncircuit in parallel with the remaining part of the arm 23 to the left'ofcontact 21, and the resistance or" this shunt circuit is such as toprovide the desired safety factor. c a a As heretofore noted, theinstrument in which the switch is used in the present instance is'acombined thermostat and humidistat. Accordingly, a humidity-sensingelement in the form of a hair rope 31 is looped over a stationary hook32 at one end of the case or cap 11 and has its free ends secured interminals which are hooked to the one end of an adjustable bracket 33.The bracket 33 is knife edged at one extremity for engagement in a notch34, formed in the adjacent top wall of the case 11 and about which thebracket pivots when adjusted. A short control shaft 35, adapted toreceive a control knob, not shown, is threaded through a bushing 36 tothe fixed adjacent wall of the casing 11 and carries a member 37 at itslower or inner end which projects through a key slot formed in thebracket 33 and engages beneath the latter.

. through an eye 41 fixed in the upper end of a hanger bracket 42, noteFIG. 5, and the latter extends through registering slots 43 and 44formed, respectively, in the top wall of the case 10 and the abutment\plate 19 and then through the slot 18 in the leaf spring blade 13, andat its lower or inner end is extended laterally beneath the said blade.Should. the moisture content or relative humidity of the air increase,the hair element will relax and permit the switch blade to flexdownwardly, and if the moisture content or the relative humiditydecreased, the

opposite effect will occur.

A temperature-responsive element is indicated at 46,

and this element, as is the case with the humidity element, is anchoredat one end to a hook 47 and at its opposite end to a bracket 47", thelatter being provided with a piv otal knife edge engaging in a notch 34'and is adjustably,

supported by means of a control or setting assembly similar in allrespects to that used for the humidity element,

and hence like parts have been given like reference numerals with theexception that a prime has been added. The center bracket indicated at48 is provided to hold the knife edge pivots of the brackets 33 and 33'e in place; it has oppositely projecting spring legs which engage inslots formed in said brackets.

A hanger'bracket 49 has its upper end connected to the bimetaltemperature element 46 by' means ofa pin and slot connection, asindicated at 50, and at its lower end projects through registering slots5-1 and 52 formed, respectively, in the top wall of the case 10' and theabutment member 19 and also through the slot 18 formed in the leafspring blade 13' and at its lower end is projected laterally forengagement beneath the said blade. Should the temperature of thesurrounding ambient air increase, I

the bimetal temperature element 46 will relax in a downward direction,and should the temperature decrease, the opposite effect will occur.

The hanger brackets 42 and 49 may be made up of a single piece ofplastic or other insulating material and assembled by inserting eachthrough the registering slots provided therefor from beneath the switchblade 13 and I Operation The switch, as exemplified herein, is of thesimple onoff type. In FIG. 10, the switch assembly is showndiagrammatically; it could be either the humidity or temperature controlswitch of FIGS. 1 to 9, inclusive, which constitute actual assemblydrawings. Here the switch blade :13, 14 and 14' of the assembly drawingsis made up of a blade proper 13A, which corresponds to the tongue 14' ofthe leaf spring type of blade of the actual switch, and a spring 14A,which corresponds to the resilient extremity 14 of the blade. Thecontact presetting and power arm or bar is indicated at 23A and theabutment member at 19A. The switch contacts and stops for the power armhave been given numbers corresponding to like parts in the assemblydrawings. in FIG. 10, the bottom of the casing functions as'the stop 26.The switch is shown controlling a motor 532 i In the position of theparts in FIGS. 10 and 10a, the contact 16 is against the on contact 21,and at this time the motor will be energized, current flowing from theline to the motor and then throughthe abutment member 19A, switch blade13A, and to the return side of the line by way of power arm 23A. FIG.=10a shows the relative positions of the parts upon closing of the motorcircuit, and FIG. 10b shortly after the motor has ben energized andcurrent flows through the power arm 23A. Note that at this time thepower arm has been deformed due to current flow, so that its freecontact-carrying extremity has moved upwardly against its stop 27 (stops26 and 27 not shown'in FIGS. la-l0d) to the point where the contact endof the switch blade lies slightly short of its throw line when moving inthe off direction, and which line passes through the pivot point 20A ofthe blade and the point of connection 54 of its spring to the hangerbracket 42 or 49. These points correspond, respectively, to the notch 20of FIG. 3 and the point where the hanger bracket 42 engages beneath theblade 13. As the free extremity 'of the power arm 23 moves upwardly orcounterclockwise, the contact 21 remains in engagement with the contact16 while at the same time the spacing between the contacts 2!]. and 22remains constant. quired to preset the switch blade 13A to this positionis furnished entirely by the power arm 23A.

FIG. c shows the relative positions of the switch blade 13A and itsassociated parts immediately following responseof the hair element to adecrease in the relative humidity of the ambient air beyond apredetermined or selected value, causing a slight upward pull on thehanger bracket 42. Since the switch blade had already been movedcounterclockwise to almost its dead-center position, the force anddistance required to trip the blade is very small. Hence the switch canbe made highly sensitive and its plus or minus tolerances reduced tomeet exacting specifications. This also provides for utilization of awider range of humidity element types than would otherwise be possible.

FIG. 10d shows the relative positions of the switch blade and itsassociated parts shortly after off contact It will be observed that theforce reis made. Since current is no longer flowing through the powerarm or bar 23A, the latter has cooled and its free extremity hasundeformed downwardly against its stop 26, presetting the blade 13Aslightly short of its throw or over-center line when the blade is movingtoward its on position. Now should the relative humidity increase aboveits selected value, the humidity element will relax and the suspensionpoint :54 will be pulled down wardly below the over-center line byspring 14A, returningrthe parts to the on position shown in FIG. 10a,completing the cycle.

In the event it is desired to use the switch to energize a controlcircuit in both switch blade positions, then the upper contact 22 needonly be wired into the other control circuit and the latter providedwith a return which by-passes the bimetal power arm or bar 23A.

What I claim is:

1. in a thermal switch for an electrical control circuit, an actuatorresponsive to a switching force, a switch-presetting arm having a freeextremity deformable as a function of current flow, a pair of spacedcontacts mounted on the free extremity of said arm, a resilient saidcontacts and arm being wired in circuit in a manner such that when oneof the switching contacts engages its coacting arm contact in a firstswitching position current flows through the arm and deforms the lattercausing its free extremity to advance said blade towards the oppositeswitching position a distance determined by said stop means to therebypreset said member adjacent one side of said throw line'ready for throwpast dead center in response to movement of said actuator, and when theother of the switching contacts engages its coacting arm contact currentflow is cut off from said arm and its free extremity moves back towardsits first switching position and repositions said switching memberadjacent the opposite side of said throw line ready for throw past deadcenter by said actuator.

2. A switch as claimed in claim '1 wherein said switch blade is anchoredat one extremity and at its opposite contact extremity is formed with anintegral prestressed bowed spring tongue having a free end edgethrusting against an abutment member approximately on the deadcenterthrow line of the blade and the switching force of said actuator isapplied to the blade back of this point of thrust in a planesubstantially parallel to blade fiexure.

3. A switch as claimed in claim 1 wherein the switch blade andcontact-presetting arm are mounted in a manner such that when theswitching and arm contacts are engaged and the armmoves to preset theswitch blade, the engaged contacts rub against one another and reducethe tendency toward contact erosion.

4. In a thermal switch for an electrical control circuit, an actuatorresponsive to a switching force, a switch-presetting arm anchored at oneextremity and having a free extremity deformable in clockwise andcounterclockwise directions as a :function of current flow, a pair ofcontacts fixed in predetermined spaced relation on the free extremity ofsaid arm, one of said contacts being electrically insulated from the armand the other contact being in conductive relation to the arm, aresilient switch blade anchored at one extremity and having a pair ofcontacts on its opposite extremity interposed between and coacting withsaid arm contacts, said blade being designed to have a snap action pasta dead-center throw line in response to movement of said actuator, stopmeans located on opposite sides of and adjacent to said throw line forlimiting the travel of said arm and the contacts carried thereby, saidcontacts and arm being Wired in circuit in a manner such that when oneof the switch blade contacts engages its coacting arm contact in a firstswitching position current flows through the arm and deforms the latterwhereupon its free extremity advances said blade toward the opmoves backtowards its undeformed position and resets said blade adjacent theopposite side of said center line for return throw past dead center bysaid actuator.

5. An instrument for switching an electrical circuit as a function ofambient air conditions, comprising: a flexible switch blade providedwith a pair of contacts and having a snap action past a dead-centerthrow line to alternate switching positions in response to a switchingforce, a blade-presetting arm at least in part deformable as a functionof current flow, said arm being anchored at on extremity and carrying onits opposite free extremity a pair of spaced contact-s, one of which iselectrically insulated from the arm and the other of which. is inelectrical con- 7 ducting relation .to the arm, said contacts and armbeing wired in circuit in a manner such that when one of the bladecontacts engages the conducting arm contact current flows through saidand deforms the latter in a direc- "tion to move the switch blade backtowards the insulated contact position and when the other blade contactengages the insulated arm cont-act current flow is cut off from said armand it undeform-s and moves the said blade back towards the insulated orconductive contact position, stop means effective to limit the travel ofsaid arm in either direction with respect to said center line, and meansresponsive to changes in ambient air conditions for snapping the bladefrom its preset position past said throw line.

6. An instrument for switching anelectrical circuit as a function ofambient air conditions, comprising: a flexible switch blade anchored atone extremity and having opother of which is in electrical conductiverelation to the arm, said blade contacts being located for alternateswitching engagement with said arm contacts, said contacts being wiredin circuit in a manner such that when one of the blade contacts engagesthe conductive arm contact current flows through said arm and deformsthe latter in a direction to move the switch blade back towards theinsulated contact position, and when the other blade contact engages theinsulated arm contact, current flow is cut off from said aim and itmoves the said blade back towards the insulated or conductive contactposition, stop means effective to limit the travel of said blade ineither direction with respect to said center line, an actuating memberengaging said blade, means responsive to changes inarnbient airconditions for applying a switching force to said actua-ting member, anda shunt circuit for limiting the flow of current through saidblade-presetting arm to a safe value.

7. In a switch for controling an electrical circuit, a pair of spacedcontacts, a resilient switch blade anchored at one extremity only andhaving a pair of contacts on its oppositeextremity interposed betweenand coacting with said spaced contacts, said blade being formed with anintegral prestressed bowed spring tongue having one end projecting free,an abutment member coaeting with said tongue in a manner such that thefree end of the latter thrusts against said abutment member at a pointapproximately on the dead-center throw line of the blade, and biases thecontact extremity of the blade toward one or the other of its alternatecontact positions, an actuator connected directly at its one extremityto an intermediate portion of said blade between said thrust point andthe anchored extremity of the blade, means responsive to changes in acondition of the ambient air directly connected to the oppositeextremity of said actuator, the switching force of said actuator beingapplied to the blade in a plane substantially parallel to the directionof blade flexure.

8. In a switch for controlling an electrical circuit as a function ofchanges in the condition of the ambient air, a housing, a pair of spacedcontacts supported by said housing, a resilient switch blade anchored atits one extremity,

to said housing and having a pair of contacts on its oppo'site extremityinterposed between and coacting with said spaced contacts, said bladebeing formed with an integral prestressed bowed spring tongue having oneend projecting tree, an abutment member coacting with said tongue andproviding a fixed thrust point for the free end of the latter 1actuator, and means accessible exteriorlyof said housing for adjustingthe tension of said humidity element.

9. A switch as claimed in claim 8 wherein a temperatureresponsiveelement is also connected directly to said actuator and there are me ansaccessible exteriorly of said housing for adjusting the temperatureresponse of said temperature element.

References (Zited in the file of this patent UNITED STATES PATENTS2,052,564 Grady Sept. 1, 1936 2,170,748 Eaton Aug. 22, 1939 2,189,996Riche Feb. 13, 1940 2,351,408 Marcy Oct. 12, 1943 2,454,320 HornbostelNov. 23, 1948 2,813,173 Risacher et a1 Nov. 12, 1957

8. IN A SWITCH FOR CONTROLLING AN ELECTRICAL CIRCUIT AS A FUNCTION OFCHANGES IN THE CONDITION OF THE AMBIENT AIR, A HOUSING, A PAIR OF SPACEDCONTACTS SUPPORTED BY SAID HOUSING, A RESILIENT SWITCH BLADE ANCHORED ATITS ONE EXTREMITY TO SAID HOUSING AND HAVING A PAIR OF CONTACTS ON ITSOPPOSITE EXTREMITY INTERPOSED BETWEEN AND COACTING WITH SAID SPACEDCONTACTS, SAID BLADE BEING FORMED WITH AN INTEGRAL PRESTRESSED BOWEDSPRING TONGUE HAVING ONE END PROJECTING FREE, AN ABUTMENT MEMBERCOACTING WITH SAID TONGUE AND PROVIDING A FIXED THRUST POINT FOR THEFREE END OF THE LATTER APPROXIMATELY ON THE DEAD-CENTER THROW LINE OFTHE BLADE TO BIAS THE CONTACT EXTREMITY OF THE BLADE TOWARD ONE OR THEOTHER OF ITS ALTERNATE CONTACT POSITIONS, AN ACTUATOR HAVING ITS ONEEXTREMITY CONNECTED DIRECTED TO AN INTERMEDIATE PORTION OF SAID BLADEBETWEEN SAID THRUST POINT AND THE ANCHORED EXTREMITY OF THE BLADE, ANELONGATED FLEXIBLE HUMIDITY-RESPONSIVE ELEMENT SUPPORTED AT ITS OPPOSITEEXTREMITIES FROM SAID HOUSING AND AT AN INTERMEDIATE POINT HAVING ACONNECTION WITH THE OPPOSITE EXTREMITY OF SAID ACTUATOR, AND MEANSACCESSIBLE EXTERIORLY OF SAID HOUSING FOR ADJUSTING THE TENSION OF SAIDHUMIDITY ELEMENT.